Inventory control

ABSTRACT

A novel encoding system, compositions for use therein and methods for determining the source, location and/or identity of a particular item or component of interest is provided. In particular, the present invention utilizes a collection of one or more sizes of populations of semiconductor nanocrystals having characteristic spectral emissions, to “track” the source or location of an item of interest or to identify a particular item of interest. The semiconductor nanocrystals used in the inventive compositions can be selected to emit a desired wavelength to produce a characteristic spectral emission in narrow spectral widths, and with a symmetric, nearly Gaussian line shape, by changing the composition and size of the semiconductor nanocrystal. Additionally, the intensity of the emission at a particular characteristic wavelength can also be varied, thus enabling the use of binary or higher order encoding schemes.

[0001] This application is a divisonal of Ser. No. 09/397,432, filed onSep. 17, 1999, which is a continuation-in-part of Ser. No. 09/160,458,filed on Sep. 24, 1998, and claims priority to the provisionalapplication Serial No. 60/101,046 entitled “Inventory Control” filed onSep. 18, 1998, each of which is incorporated in its entirety byreference. This application is related to the following applicationwhich was filed Sep. 24, 1998 and which is incorporated in its entiretyby reference: application Ser. No. 09/160,454 entitled “BiologicalApplications of Quantum Dots”. Additionally, this application is alsorelated to the following application, which was filed on Sep. 18, 1998,and which is incorporated in its entirety by reference: application Ser.No. 09/156,863 entitled “Water Soluble Luminescent Nanocrystals”.

[0002] This invention was made with U.S. government support underContract Number 94-00334 awarded by the National Science Foundation. TheU.S. government has certain rights in the invention

[0003] A portion of the disclosure of this patent document containsmaterial that is subject to copyright protection. The copyright ownerhas no objection to the reproduction by anyone of the patent document orthe patent disclosure, as it appears in the Patent and Trademark Officepatent file or records, but otherwise reserves all copyright rightswhatsoever.

BACKGROUND OF THE INVENTION

[0004] The ability to track the location or identity of a component oritem of interest has presented a significant challenge for industry andscience. For example, the demands of keeping track of consumer products,such as items in a grocery store or jewelry, and the interest inidentification devices, such as security cards, has led to the need fora secure and convenient system. Additionally, emerging technologies suchas combinatorial chemistry, genomics research, and microfluidics alsorequire the ability to identify and track the location of large numbersof items.

[0005] A traditionally used method for tracking the location or identityof a component or item of interest is Universal Product Code technology,or barcode technology, which uses a linear array of elements that areeither printed directly on an object or on labels that are affixed tothe object. These bar code elements typically comprise bars and spaces,with bars of varying widths representing strings of binary ones andspaces of varying widths representing strings of binary zeros. Bar codescan be detectable optically using devices such as scanning laser beamsor handheld wands, or they can be implemented in magnetic media. Thereaders and scanning systems electro-optically decode the symbol tomultiple alphanumerical characters that are intended to be descriptiveof the article or some characteristic thereof. Such characters aretypically represented in digital form as an input to a data processingsystem for applications in point-of-sale processing and inventorycontrol to name a few.

[0006] Although traditional bar codes typically only contain five or sixletters or digits, two dimensional barcodes have also been developed inwhich one-dimensional bar codes are stacked with horizontal guard barsbetween them to increase the information density. For example, U.S. Pat.No. 5,304,786 describes the use of a high-density two-dimensional barcode symbol for use in bar code applications. Unfortunately, althoughthe information density of barcode technology has improved, thistechnology is often easily destructible, and the interference of dust,dirt and physical damage limits the accuracy of the information acquiredfrom the readout equipment. Additionally, because of the difficulty ofetching the barcode on many items, it is also difficult to apply to awide range of uses.

[0007] Another technology that has been developed for labeling objectsincludes a composition comprising silicon or silicon dioxidemicroparticles and a powder, fluid or gas to be applied to objects suchas vehicles, credit cards and jewelry (WO 95/29437). This systemtypically allows the formation of 200 million particles on a singlewafer, each of the particles on one wafer being designed to be ofidentical shape and size so that when the particles are freed from thewafer substrate one is left with a suspension containing a singleparticle type which can thus be identified and associated with aparticular item of interest.

[0008] This system, although information dense, is also not practicalfor a wide range of application. One of the advantages explicitly statedin the application includes the unlikely event of unauthorizedreplication of the particles because of the non-trivial process ofmicromachining used, which requires specialized equipment and skills.Thus, this process would not be widely amenable to a range of uses forinventory control.

[0009] In addition to above-mentioned barcoding and microparticleinventory control schemes, emerging technologies such as combinatorialchemistry have also resulted in the development of various encodingschemes (See, for example, Czarnik, A. W., “Encoding Methods forCombinatorial Chemistry”, Curr. Opin. Chem. Biol., 1997, 1, 60). Theneed for this development has arisen in part from the split and pooltechnique utilized in combinatorial chemistry to generate libraries onthe order of one million compounds. Split and pool synthesis involvesdividing a collection in beads into N groups, where N represents thenumber of different reagents being used in a particular reaction stage,and after the reaction is performed, pooling all of these groupstogether and repeating the split and pool process until the desiredreaction sequence is completed. Clearly, in order to keep track of eachof the compounds produced from a reaction series, the beads must be“tagged” or encoded with information at each stage to enableidentification of the compound of interest or the reaction pathwayproducing the compound. The tags used to encode the information,however, must be robust to the conditions being employed in the chemicalsynthesis and must be easily identifiable to obtain the information.Exemplary encoding techniques that have been developed include the useof chemically robust small organic molecules (“tags”) that are cleavedfrom the bead after the synthesis is completed and analyzed using massspectroscopy. (U.S. Pat. No. 5,565,324; U.S. Pat. No. 5,721,099). Thedisadvantage of this method is that the “tags” must be cleaved from thebead in order to gain information about the identity of the compound ofinterest.

[0010] In response to this, several groups have developed encodingschemes that allow analysis while the “tags” are still attached to thesupports. For example, Radiofrequency Encoded Combinatorial (REC™)chemistry combines recent advances in microelectronics, sensors, andchemistry and uses a Single or Multiple Addressable Radiofrequency Tag(SMART™) semiconductor unit to record encoding and other relevantinformation along the synthetic pathway (Nicolaou et al., Angew. Chem.Int. Ed. Engl. 1995, 34, 2289). The disadvantage of this system,however, is that the SMART™ memory devices utilized are very large insize (mm), and thus scanning the bead to decode the information becomesdifficult. Another example of on-bead decoding includes the use ofcolored and fluorescent beads (Egner et al., Chem. Commun. 1997, 735),in which a confocal microscope laser system was used to obtain thefluorescence spectra of fluorescent dyes. The drawback of this method,however, is the tendency of the dyes to undergo internal quenching byeither energy transfer or reabsorption of the emitted light.Additionally, this system is not able to identify uniquely anddistinctly a range of dyes.

[0011] Clearly, it would be desirable to develop a general informationdense encoding system flexible, robust and practical enough to beutilized both in general inventory control and in emerging technologies.This system would also be capable of distinctly and uniquely identifyingparticular items or components of interest.

SUMMARY OF THE INVENTION

[0012] The present invention provides a novel encoding system andmethods for determining the location and/or identity of a particularitem or component of interest. In particular, the present inventionutilizes a “barcode” comprising one or more particle size distributionsof semiconductor nanocrystals (also known as a Quantum Dot™ particles)having characteristic spectral emissions to either “track” the locationor source of a particular item of interest or to identify a particularitem of interest. The semiconductor nanocrystals used in the inventive“barcoding” scheme can be tuned to a desired wavelength to produce acharacteristic spectral emission by changing the composition and size,or size distribution, of the semiconductor nanocrystal. Additionally,the intensity of the emission at a particular characteristic wavelengthcan also be varied, thus enabling the use of binary or higher orderencoding schemes. The information encoded by the semiconductornanocrystal can be spectroscopically decoded, thus providing thelocation, source and/or identity of the particular item or component ofinterest.

[0013] In a particularly preferred embodiment, the method involvesproviding a composition comprising an item of interest, and one or morecompositions (e.g., composition of core and or shell), sizes or sizedistributions of semiconductor nanocrystals having characteristicspectral emissions, or providing a composition comprising a support, anitem of interest, and one or more sizes of semiconductor nanocrystals;subjecting said composition to a primary light source to obtain thespectral emissions for said one or more sizes of semiconductornanocrystals on said composition; and correlating said spectral emissionwith said item of interest. The present method, in preferredembodiments, can be used to encode the identity of biomolecules,particularly DNA sequences, or other items, including, but not limitedto, consumer products, identification tags and fluids.

[0014] In another aspect, the present invention provides compositions.In one particularly preferred embodiment, the composition comprises asupport, and one or more particle size distributions of semiconductornanocrystals having different characteristic spectral emissions. Inanother particularly preferred embodiment, the composition comprises asupport, one or more items of interest and one or more sizes ofsemiconductor nanocrystals having different characteristic spectralemissions. In yet another preferred embodiment, the compositioncomprises an item of interest and one or more sizes of semiconductornanocrystals having different characteristic spectral emissions. Thesemiconductor nanocrystals can be associated with, attached thereto, orembedded within said support structure. Additionally, the semiconductornanocrystal can optionally have an overcoating comprised of a materialhaving a band gap greater than that of the semiconductor nanocrystal.

[0015] In yet another aspect, the present invention provides librariesof compounds and/or items of interest. In a particularly preferredembodiment, each compound in the library is bound to an individualsupport, and each support has attached thereto or embedded therein oneor more identifiers comprising one or more particle size distributionsof semiconductor nanocrystals having characteristic spectral emissions.In yet another preferred embodiment, each item of interest has attachedthereto, or embedded therein one or more identifiers comprising one ormore particle size distributions of semiconductor nanocrystals havingcharacteristic spectral emissions.

[0016] In yet another aspect, the present invention also provides kitsfor identifying an item of interest comprising a collection of items ofinterest, and wherein each member of said collection of objects hasattached thereto or embedded therein one or more particle sizedistributions of semiconductor nanocrystals having characteristicspectral emissions. In another preferred embodiment, the kit comprises acollection of items of interest, each bound to a solid support, whereineach support has attached thereto, associated therewith, or embeddedtherein one or more unique identifiers.

[0017] In another aspect, the present invention provides methods foridentifying a compound having a particular characteristic of interestcomprising providing a library of compounds, testing said library ofcompounds for a particular characteristic of interest, observing thephotoluminescence spectrum for each identifier attached to each supportcontaining a compound of interest, and identifying the compound ofinterest by determining the reaction sequence as encoded by said one ormore sizes of semiconductor nanocrystals. In yet another particularlypreferred embodiment, the step of identifying the reaction sequence canbe determined before testing the library of compounds because thereaction sequence can be recorded during the synthesis of the compoundby “reading” the beads (i.e., observing the photoluminescence spectrum)prior to each reaction step to record the reaction stages. The presentinvention additionally provides methods for recording the reactionstages of a synthesis concurrently with the synthesis.

[0018] In yet another aspect, the present invention provides methods foridentifying a molecule having a characteristic of interest comprisingcontacting a first library of molecules with a second library ofmolecules, wherein each of the molecules in the first library is encodedusing one or more sizes of semiconductor nanocrystals and the secondlibrary has attached thereto or embedded therein one or more sizes ofsemiconductor nanocrystals acting as “probes”. This method providessimultaneously a way to identify the binding of one or more moleculesfrom the second library to the first library and determining thestructure of said one or more molecules from the first library.

[0019] In one aspect of the invention a composition is providedcomprising of one or more populations of member semiconductornanocrystals, wherein each population has a distinct characteristicspectral emission.

[0020] In another aspect of the invention, a composition is providedcomprising the aforementioned populations of nanocrystals associatedwith a support.

[0021] In yet another aspect of the invention, a composition is providedcomprising the aforementioned populations of nanocrystals associatedwith an item of interest, preferably the nanocrystals are associatedwith a support.

[0022] In still another aspect of the invention, a library of compoundsis provided, wherein each compound in the library is bound to anindividual support, each support having associated therewith one or morepopulations of semiconductor nanocrystals, each population having adistinct characteristic spectral emissions.

[0023] In a further aspect of the invention, a method is provided foridentifying a compound having a characteristic of interest. The methodcomprises (a) providing a library of member compounds, wherein eachmember of said library of compounds is attached to a support, andwherein each support also has attached thereto or embedded therein oneor more populations of semiconductor nanocrystals each population havingdistinct characteristic spectral emissions, (b) testing each member ofsaid library of compounds to identify compounds having a characteristicof interest, (c) subjecting each support to a light source to obtain thecharacteristic spectral emission, and (d) correlating the spectralemission with the identity of the compound having the characteristic ofinterest.

[0024] In yet a further aspect of the invention, a method is foridentifying a molecule having a characteristic of interest. The methodcomprises (a) providing a first library of one or more member molecules,wherein each member of said first library is attached to a first supporthaving attached thereto or embedded therein one or more firstpopulations of semiconductor nanocrystals, each first population havinga distinct characteristic first spectral emission, (b) providing asecond library of one or more member molecules, wherein each member ofsaid second library is attached to a second support having attachedthereto or embedded therein one or more second populations ofsemiconductor nanocrystals, each second population having a distinctcharacteristic second spectral emission, and wherein the second spectralemission is distinct from the first spectral emission, (c) contactingsaid first library of molecules with said second library of molecules,and (d) observing the first and second spectral emissions, wherein saidfirst and second spectral emissions provide information about which ofthe molecules from the second library of molecules are associated withsaid first library of molecules, and provides information about theidentity of the molecule from said first library of molecules.

[0025] These and other embodiments and aspects of the present inventionwill readily occur to those of ordinary skill in the art in view of thedisclosure herein.

DESCRIPTION OF THE DRAWING

[0026] The file of this patent contains at least one drawing executed incolor. Copies of this patent with color drawing(s) will be provided bythe Patent and Trademark Office upon request and payment of thenecessary fee.

[0027]FIG. 1 depicts a color photograph of several suspensions ofdifferent sizes of ZnS overcoated CdSe semiconductor nanocrystals inhexane, illustrating the wide range of colors that can be utilized inthe present invention.

[0028]FIG. 2 depicts a general displacement reaction to modify thesurface of the semiconductor nanocrystal.

[0029]FIG. 3 depicts the use of the inventive system in fluid dynamics.

[0030]FIG. 4 depicts the use of the inventive system in theidentification of an object of interest.

[0031]FIG. 5 depicts the use of the inventive system in the encoding ofcombinatorial libraries.

DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

[0032] Definitions and Nomenclature:

[0033] Before the present invention is disclosed and described indetail, it is to be understood that this invention is not limited tospecific assay formats, materials or reagents, as such may, of course,vary. It is also to be understood that the terminology used herein isfor describing particular embodiments only and is not intended to belimiting.

[0034] It must be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to “a nanocrystal” includes more than onenanocrystal, reference to “an oligonucleotide” includes more than onesuch oligonucleotide, and the like.

[0035] In this specification and in the claims that follow, referencewill be made to a number of terms that shall be defined to have thefollowing meanings:

[0036] “Quantum Dot™ particle”: As used herein, the term “Quantum Dot™particle” includes a semiconductor nanocrystal with size dependentoptical and electrical properties. In particular, the band gap energy ofa semiconductor nanocrystal varies with the diameter of the crystal.

[0037] “Semiconductor nanocrystal” includes, for example, inorganiccrystallites between about 1 nm and about 1000 nm in diameter,preferably between about 2 nm and about 50 nm, more preferably about 5nm to about 20 nm (such as about 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19, or 20 nm) that includes a “core” of one or more firstsemiconductor materials, and which may be surrounded by a “shell” of asecond semiconductor material. A semiconductor nanocrystal coresurrounded by a semiconductor shell is referred to as a “core/shell”semiconductor nanocrystal. The surrounding “shell” material willpreferably have a bandgap greater than the bandgap of the core materialand can be chosen so to have an atomic spacing close to that of the“core” substrate. The core and/or the shell can be a semiconductormaterial including, but not limited to, those of the group II-VI (ZnS,ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, MgTe and the like) andIII-V (GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlAs, AlP, AlSb, AlS,and the like) and IV (Ge, Si, Pb and the like) materials, and an alloythereof, or a mixture thereof.

[0038] A semiconductor nanocrystal is, optionally, surrounded by a“coat” of an organic capping agent. The organic capping agent may be anynumber of materials, but has an affinity for the semiconductornanocrystal surface. In general, the capping agent can be an isolatedorganic molecule, a polymer (or a monomer for a polymerizationreaction), an inorganic complex, and an extended crystalline structure.The coat is used to convey solubility, e.g., the ability to disperse acoated semiconductor nanocrystal homogeneously into a chosen solvent,functionality, binding properties, or the like. In addition, the coatcan be used to tailor the optical properties of the semiconductornanocrystal.

[0039] “Identification unit or barcode”: As used herein, the term“identification unit” is used synonymously with the term “barcode”, andcomprises one or more sizes of semiconductor nanocrystals, each size ofsemiconductor nanocrystal having a characteristic emission spectrum. The“identification unit” or “barcode” enables the determination of thelocation or identity of a particular item or matter of interest.

[0040] “Item of interest”: As used herein, the term “item of interest”is used synonymously with the term “component of interest” and refers toany item, including, but not limited to, consumer item, fluid, gas,solid, chemical compound, and biomolecule.

[0041] “Biomolecule”: As used herein, the term “biomolecule” refers tomolecules (e.g., proteins, amino acids, nucleic acids, nucleotides,carbohydrates, sugars, lipids, etc.) that are found in nature.

[0042] The terms “polynucleotide,” “oligonucleotide,” “nucleic acid” and“nucleic acid molecule” as used herein to include a polymeric form ofnucleotides of any length, either ribonucleotides ordeoxyribonucleotides. This term refers only to the primary structure ofthe molecule. Thus, the term includes triple-, double- andsingle-stranded DNA, as well as triple-, double- and single-strandedRNA. It also includes modifications, such as by methylation and/or bycapping, and unmodified forms of the polynucleotide.

[0043] More particularly, the terms “polynucleotide,” “oligonucleotide,”“nucleic acid” and “nucleic acid molecule” includepolydeoxyribonucleotides (containing 2-deoxy-D-ribose),polyribonucleotides (containing D-ribose), any other type ofpolynucleotide which is an Nor C-glycoside of a purine or pyrimidinebase, and other polymers containing normucleotidic backbones, forexample, polyamide (e.g., peptide nucleic acids (PNAs)) andpolymorpholino (commercially available from the Anti-Virals, Inc.,Corvallis, Oreg., as Neugene) polymers, and other syntheticsequence-specific nucleic acid polymers providing that the polymerscontain nucleobases in a configuration which allows for base pairing andbase stacking, such as is found in DNA and RNA. There is no intendeddistinction in length between the terms “polynucleotide,”“oligonucleotide,” “nucleic acid” and “nucleic acid molecule,” and theseterms will be used interchangeably. These terms refer only to theprimary structure of the molecule. Thus, these terms include, forexample, 3′-deoxy-2′,5′-DNA, oligodeoxyribonucleotide N3′ P5′phosphoramidates, 2′-O-alkyl-substituted RNA, triple-, double- andsingle-stranded DNA, as well as triple-, double- and single-strandedRNA, DNA:RNA hybrids, and hybrids between PNAs and DNA or RNA, and alsoinclude known types of modifications, for example, labels which areknown in the art, methylation, “caps,” substitution of one or more ofthe naturally occurring nucleotides with an analog, internucleotidemodifications such as, for example, those with uncharged linkages (e.g.,methyl phosphonates, phosphotriesters, phosphoramidates, carbamates,etc.), with negatively charged linkages (e.g., phosphorothioates,phosphorodithioates, etc.), and with positively charged linkages (e.g.,aminoalklyphosphoramidates, aminoalkylphosphotriesters), thosecontaining pendant moieties, such as, for example, proteins (includingnucleases, toxins, antibodies, signal peptides, poly-L-lysine, etc.),those with intercalators (e.g., acridine, psoralen, etc.), thosecontaining chelators (e.g., metals, radioactive metals, boron, oxidativemetals, etc.), those containing alkylators, those with modified linkages(e.g., alpha anomeric nucleic acids, etc.), as well as unmodified formsof the polynucleotide or oligonucleotide. In particular, DNA isdeoxyribonucleic acid.

[0044] “Polypeptide” and “protein” are used interchangeably herein andinclude a molecular chain of amino acids linked through peptide bonds.The terms do not refer to a specific length of the product. Thus,“peptides,” “oligopeptides,” and “proteins” are included within thedefinition of polypeptide. The terms include post-translationalmodifications of the polypeptide, for example, glycosylations,acetylations, phosphorylations and the like. In addition, proteinfragments, analogs, mutated or variant proteins, fusion proteins and thelike are included within the meaning of polypeptide.

[0045] The term “sugar moiety” includes reference to monosaccharides,disaccharides, polysaccharides, and the like. The term “sugar” includesthose moieties which have been modified, e.g., wherein one or more ofthe hydroxyl groups are replaced with halogen, alkoxy moieties,aliphatic groups, or are functionalized as ethers, amines, or the like.Examples of modified sugars include: those which contain a lower alkoxygroup in place of a hydroxyl moiety, i.e., α- or β-glycosides such asmethyl α-D-glucopyranoside, methyl β-D-glucopyranoside, and the like;those which have been reacted with amines, i.e., N-glycosylamines orN-glycosides such as N-α-D-glucopyranosyl)methylamine; those containingacylated hydroxyl groups, typically from 1 to 5 lower acyl groups; thosecontaining one or more carboxylic acid groups, e.g., D-gluconic acid orthe like; and those containing free amine groups such as D-glucosamine,D-galactosamine, N-acetyl-D-glucosamine or the like. Examples ofpreferred saccharides are glucose, galactose, fructose, ribose, mannose,arabinose, and xylose. Examples of polysaccharides is dextran andcellulose.

[0046] “One or more sizes of semiconductor nanocrystals”: As usedherein, the phrase “one or more sizes of semiconductor nanocrystals” isused synonymously with the phrase “one or more particle sizedistributions of semiconductor nanocrystals”. One of ordinary skill inthe art will realize that particular sizes of semiconductor nanocrystalsare actually obtained as particle size distributions.

[0047] The phrase “associated with” is used herein to indicate itemsthat are physically linked by, for example, covalent chemical bonds,physical forces such van der Waals or hydrophbic interactions,encapsulation, embedding, or the like. The phrase “associated with” alsointends maintaining a correspondence between items by other thanphysical linkage, e.g., through the use of a look-up table or othermethod of recording the association/correspondence.

[0048] As used herein, the term “binding pair” refers first and secondmolecules that specifically bind to each other. “Specific binding” ofthe first member of the binding pair to the second member of the bindingpair in a sample is evidenced by the binding of the first member to thesecond member, or vice versa, with greater affinity and specificity thanto other components in the sample. The binding between the members ofthe binding pair is typically non-covalent. The terms “affinitymolecule” and “target analyte” are used herein to refer to first andsecond members of a binding pair, respectively.

[0049] Exemplary binding pairs include any haptenic or antigeniccompound in combination with a corresponding antibody or binding portionor fragment thereof (e.g., digoxigenin and anti-digoxigenin; mouseimmunoglobulin and goat anti-mouse immunoglobulin) and nonimmunologicalbinding pairs (e.g., biotin-avidin, biotinstrepavidin, hormone [e.g.,thyroxine and cortisol]-hormone binding protein, receptor-receptoragonist or antagonist (e.g., acetylcholine receptor-acetylcholine or ananalog thereof) IgG-protein A, lectin-carbohydrate, enzyme-enzymecofactor, enzyme-enzyme-inhibitor, and complementary polynucleotidepairs capable of forming nucleic acid duplexes) and the like.

[0050] “Optional” or “optionally” means that the subsequently describedevent or circumstance may or may not occur, and that the descriptionincludes instances where said event or circumstance occurs and instanceswhere it does not. For example, the phrase “optionally having anovercoating” means that an overcoating may or may not be present andthat the description includes both where there is and where there is notan overcoating, and the like.

[0051] Recognizing the need to identify and locate specific items orcomponents of interest, the present invention provides a novel encodingsystem. In particular, the present invention utilizes a “barcode”comprising one or more particle size distributions of semiconductornanocrystals, having characteristic spectral emissions, to either“track” the location of a particular item of interest or to identify aparticular item of interest. The semiconductor nanocrystals used in theinventive “barcoding” scheme can be tuned to a desired wavelength toproduce a characteristic spectral emission by changing the compositionand size of the semiconductor nanocrystal, and additionally, theintensity of the emission at a particular characteristic wavelength canalso be varied, thus enabling the use of binary or higher order encodingschemes. The information encoded by the semiconductor nanocrystals canbe spectroscopically decoded, thus providing the location and/oridentity of the particular item or component of interest.

[0052] The ability of the semiconductor nanocrystals to be utilized inthe inventive barcode system results from their unique characteristics.Semiconductor nanocrystals have radii that are smaller than the bulkexciton Bohr radius and constitute a class of materials intermediatebetween molecular and bulk forms of matter. Quantum confinement of boththe electron and hole in all three dimensions leads to an increase inthe effective band gap of the material with decreasing crystallite size.Consequently, both the optical absorption and emission of semiconductornanocrystals shift to the blue (higher energies). Upon exposure to aprimary light source, each semiconductor nanocrystal distribution iscapable of emitting energy in narrow spectral linewidths, as narrow as25-30 nm, and with a symmetric, nearly Gaussian line shape, thusproviding an easy way to identify a particular semiconductornanocrystal. As one of ordinary skill in the art will realize, thelinewidths are dependent on the size heterogeneity, i.e.,monodispersity, of the semiconductor nanocrystals in each preparation.Single semiconductor nanocrystal complexes have been observed to havefull width at half max (FWHM) as narrow as 12-15 nm. In addition,semiconductor nanocrystal distributions with larger linewidths in therange of 40-60 nm can be readily made and have the same physicalcharacteristics as semiconductor nanocrystals with narrower linewidths.Exemplary materials for use as semiconductor nanocrystals in the presentinvention include, but are not limited to group II-IV, III-V and groupIV semiconductors such as ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, GaN, GaP,GaAs, GaSb, InP, InAs, InSb, AlS, AlP, AlSb, PbS, PbSe, Ge and Si andternary and quaternary mixtures thereof. The semiconductor nanocrystalsare characterized by their uniform nanometer size. By “nanometer” size,it is meant less than about 150 Angstroms (A), and preferably in therange of 12-150 A.

[0053] As discussed above, the selection of the composition of thesemiconductor nanocrystal, as well as the size of the semiconductornanocrystal, affects the characteristic spectral emission wavelength ofthe semiconductor nanocrystal. Thus, as one of ordinary skill in the artwill realize, a particular composition of a semiconductor nanocrystal aslisted above will be selected based upon the spectral region beingmonitored. For example, semiconductor nanocrystals that emit energy inthe visible range include, but are not limited to CdS, CdSe, CdTe, ZnSe,ZnTe, GaP, and GaAs. FIG. 1 depicts a color photograph of severalsuspensions of different sizes of ZnS overcoated CdSe semiconductornanocrystals in hexane illustrating the wide range of colors availablefor use in the present invention. Semiconductor nanocrystals that emitenergy in the near IR range include, but are not limited to, InP, InAs,InSb, PbS, and PbSe. Finally, semiconductor nanocrystals that emitenergy in the blue to near-ultraviolet include, but are not limited toZnS and GaN. For any particular composition selected for thesemiconductor nanocrystals to be used in the inventive system, it ispossible to tune the emission to a desired wavelength by controlling thesize of the particular composition of the semiconductor nanocrystal. Inpreferred embodiments, 5-20 discrete emissions (five to twenty differentsize populations or distributions distinguishable from one another) areobtained for any particular composition, although one of ordinary skillin the art will realize that fewer than five emissions and more thantwenty emissions could be used depending on the monodispersity of thesemiconductor nanocrystal particles. If high information density isrequired, and thus a greater number of distinct emissions, thenanocrystals are also substantially monodisperse within the broadnanometer range given above (12-150 A). By monodisperse, as that term isused herein, it means a colloidal system in which the suspendedparticles have substantially identical size and shape. In preferredembodiments for high information density applications, monodisperseparticles deviate less than 10% rms in diameter, and preferably lessthan 5%. Monodisperse semiconductor nanocrystals have been described indetail in Murray et al. (J. Am. Chem. Soc., 1993, 115, 8706), and in thethesis of Christopher Murray, “Synthesis and Characterization of II-VIQuantum Dots and Their Assembly into 3-D Quantum Dot Superlattices”,Massachusetts Institute of Technology, September, 1995, which are herebyincorporated in their entireties by reference. One of ordinary skill inthe art will also realize that the number of discrete emissions that canbe distinctly observed for a given composition depends not only upon themonodispersity of the particles, but also on the deconvolutiontechniques employed. Semiconductor nanocrystals, unlike dye molecules,can be easily modeled as Gaussians and therefore are more easily andmore accurately deconvoluted.

[0054] However, for some applications high information density will notbe required and it may be more economically attractive to use morepolydisperse particles. Thus, for applications that do not require highinformation density, the linewidth of the emission may be in the rangeof 40-60 nm.

[0055] In addition to the ability to tune the emission energy bycontrolling the size of the particular semiconductor nanocrystal, theintensities of that particular emission observed at a specificwavelength are also capable of being varied, thus increasing thepotential information density provided by the semiconductor nanocrystal“barcode” system. In preferred embodiments, 2-15 different intensitiesmay be achieved for a particular emission at a desired wavelength,however, one of ordinary skill in the art will realize that more thanfifteen different intensities may be achieved, depending upon theparticular application of the inventive identification units. For thepurposes of the present invention, different intensities may be achievedby varying the concentrations of the particular size semiconductornanocrystal attached to, embedded within or associated with an item orcomponent of interest.

[0056] In a particularly preferred embodiment, the surface of thesemiconductor nanocrystal is also modified to enhance the efficiency ofthe emissions, by adding an overcoating layer to the semiconductornanocrystal. The overcoating layer is particularly preferred because atthe surface of the semiconductor nanocrystal, surface defects can resultin traps for electron or holes that degrade the electrical and opticalproperties of the semiconductor nanocrystal. An insulating layer at thesurface of the semiconductor nanocrystal provides an atomically abruptjump in the chemical potential at the interface that eliminates energystates that can serve as traps for the electrons and holes. This resultsin higher efficiency in the luminescent process.

[0057] Suitable materials for the overcoating layer includesemiconductors having a higher band gap energy than the semiconductornanocrystal. In addition to having a band gap energy greater than thesemiconductor nanocrystals, suitable materials for the overcoating layershould have good conduction and valence band offset with respect to thesemiconductor nanocrystal. Thus, the conduction band is desirably higherand the valence band is desirably lower than those of the semiconductornanocrystal. For semiconductor nanocrystals that emit energy in thevisible (e.g., CdS, CdSe, CdTe, ZnSe, ZnTe, GaP, GaAs) or near IR (e.g.,InP, InAs, InSb, PbS, PbSe), a material that has a band gap energy inthe ultraviolet regions may be used. Exemplary materials include ZnS,GaN, and magnesium chalcogenides, e.g., MgS, MgSe, and MgTe. Forsemiconductor nanocrystals that emit in the near IR, materials having aband gap energy in the visible, such as CdS or CdSe, may also be used.The overcoating layer may include as many as eight monolayers of thesemiconductor material. The preparation of a coated semiconductornanocrystal may be found in U.S. Ser. No. 08/969,302, filed Nov. 13,1997 and entitled “Highly Luminescent Color-Selective Materials”, andDabbousi et al., (J. Phys. Chem. B, 1997, 101, 9463) and Kuno et al.,(J. Phys. Chem., 1997, 106, 9869).

[0058] After selection of a particular collection of semiconductornanocrystal composition and sizes as discussed above to associate withan item of interest, the semiconductor nanocrystals can be attached to,embedded within or associated with that particular item of interest. Asone of ordinary skill in the art will realize, the item of interest mustbe sufficiently reactive with the surface of the semiconductornanocrystal, or must be sufficiently compatible with the semiconductornanocrystal.

[0059] Most semiconductor nanocrystals are prepared in coordinatingsolvent, such as trioctylphosphine oxide (TOPO) and trioctyl phosphine(TOP) resulting in the formation of a passivating organic layer on thedot surface comprised of the organic solvent. This layer is present onsemiconductor nanocrystals containing an overcoating and those that donot contain an overcoating. Thus, either of these classes of passivatedsemiconductor nanocrystals are readily soluble in organic solvents, suchas toluene, chloroform and hexane. As one of ordinary skill in the artwill realize, these functional moieties may be readily displaced ormodified to provide an outer coating that renders the semiconductornanocrystals suitable for use as the identification units of the presentinvention.

[0060] Furthermore, based upon the desired application, a portion of thesemiconductor nanocrystal functionality, or the entire surface of thesemiconductor nanocrystal functionality may be modified by adisplacement reaction, based upon the desired application of theinventive identification units. FIG. 2 depicts general displacementreactions of certain functional moieties to provide a semiconductornanocrystals with modified functionalities for use in the inventivemethod. FIG. 2 also depicts the ability to displace a specificpercentage of moieties on the surface of the semiconductor nanocrystals.For example, reaction A, depicts the partial displacement of moiety X bymoiety Y, whereas reaction B depicts the complete displacement of moietyX by moiety Y for a semiconductor nanocrystal having no overcoatinglayer. Reactions C and D depict the partial and complete displacementreactions for overcoated semiconductor nanocrystals, respectively. Ingeneral, moieties such as TOPO and TOP, as well as other moieties may bereadily displaced and replaced with other functional moieties,including, but not limited to carboxylic acids, amines, aldehydes, andstyrene to name a few. One of ordinary skill in the art will realizethat factors relevant to the success of a particular displacementreaction include the concentration of the replacement moiety,temperature and reactivity. Thus, for the purposes of the presentinvention, any functional moiety may be utilized that is capable ofdisplacing an existing functional moiety to provide a semiconductornanocrystal with a modified functionality for a specific use of theidentification units of the present invention.

[0061] The ability to utilize a general displacement reaction to modifyselectively the surface functionality of the semiconductor nanocrystalsenables functionalization for specific uses of the inventiveidentification units. In one particularly preferred embodiment, watersoluble semiconductor nanocrystals are provided for use in aqueousenvironments. In the case of water-soluble semiconductor nanocrystals,the outer layer includes a compound having at least one linking moietythat attaches to the surface of the particle and that terminates in atleast one hydrophilic moiety. The linking and hydrophilic moieties arespanned by a hydrophobic region sufficient to prevent charge transferacross the region. The hydrophobic region also provides a“pseudo-hydrophobic” environment for the nanocrystal and thereby shieldsit from aqueous surroundings. A detailed description of methods formaking water soluble semiconductor nanocrystals may be found in theapplication entitled “Water Soluble Luminescent Nanocrystals” filed thesame day herewith, and incorporated in its entirety by reference. Inpreferred embodiments, the hydrophilic moiety may be a polar or charged(positive or negative) group. The polarity or charge of the groupprovides the necessary hydrophilic interactions with water to providestable solutions or suspensions of the semiconductor nanocrystal.Exemplary hydrophilic groups include polar groups such as hydroxides(—OH), amines, polyethers, such as polyethylene glycol and the like, aswell as charged groups, such as carboxylates (—CO²—), sulfonates (SO₃—),phosphates (—PO₄ ²⁻ and PO₃ ²⁻), nitrates, ammonium salts (—NH₄ ⁺), andthe like.

[0062] In another particularly preferred embodiment, a displacementreaction may be employed to modify the semiconductor nanocrystal toimprove the solubility in a particular organic solvent. For example, ifit is desired to associate the semiconductor nanocrystals with aparticular solvent or liquid, such as pyridine, the surface can bespecifically modified with pyridine or pyridine-like moieties to ensuresolvation.

[0063] In yet another particularly preferred embodiment, the surfacelayer is modified by displacement to render the semiconductornanocrystal reactive for a particular coupling reaction. For example,displacement of TOPO moieties with a group containing a carboxylic acidmoiety enables the reaction of the modified semiconductor nanocrystalswith amine containing moieties (commonly found on solid support units)to provide an amide linkage.

[0064] Likewise, the surface of the semiconductor nanocrystal can alsobe modified to create a surface on the semiconductor nanocrystal similarto an object that the semiconductor nanocrystal will be associated with.For example, the semiconductor nanocrystal surface can be modified usinga displacement reaction to create styrene or acrylate moieties, thusenabling the incorporation of the semiconductor nanocrystals intopolystyrene, polyacrylate or other polymers such as polymer, such aspolyimide, polyacrylamide, polyethylene, polyvinyl, poly-diacetylene,polyphenylene-vinylene, polypeptide, polysaccharide, polysulfone,polypyrrole, polyimidazole, polythiophene, polyether, epoxies, silicaglass, silica gel, siloxane, polyphosphate, hydrogel, agarose,cellulose, and the like.

[0065] After selection of the composition of semiconductor nanocrystalfor the desired range of spectral emission and selection of a desiredsurface functionalization compatible with the system of interest, it mayalso be desirable to select the minimum number of semiconductornanocrystals needed to observe a distinct and unique spectral emissionof sufficient intensity for spectral identification. Selection criteriaimportant in determining the minimum number of semiconductornanocrystals needed to observe a distinct and unique spectral emissionof sufficient intensity include providing a sufficient number ofsemiconductor nanocrystals that are bright (i.e., that emit light versusthose that are dark) and providing a sufficient number of semiconductornanocrystals to average out over the blinking effect observed in singlesemiconductor nanocrystal emissions (M. Nirmal et al., Nature, 1996,383, 802). In one particularly preferred embodiment, at least eightsemiconductor nanocrystals of a particular composition and particle sizedistribution are provided. For example, if a “barcode” were providedthat utilized three different particle size distributions of aparticular composition, it would be most desirable to utilize eight ofeach of the three different particle size distributions of asemiconductor nanocrystal, in order to observe sufficiently intensespectral emissions from each to provide reliable information regardingthe location or identity of a particular item or matter of interest. Oneof ordinary skill in the art will realize, however, that fewer thaneight semiconductor nanocrystals of a particular composition andparticle size distribution could be utilized provided that a uniquespectral emission of sufficient intensity is observed, as determined bythe selection criteria set forth above.

[0066] As discussed previously, the ability of the semiconductornanocrystals to produce discrete optical transitions, along with theability to vary the intensity of these optical transitions, enables thedevelopment of a versatile and dense encoding scheme. The characteristicemissions produced by one or more sizes of semiconductor nanocrystalsattached to, associated with, or embedded within a particular support ormatter enables the identification of the item or composition of interestand/or its location. For example, by providing N sizes of semiconductornanocrystals (each having a discrete optical transition), each having Mdistinguishable states resulting from the absence of the semiconductornanocrystal, or from different intensities resulting from a particulardiscrete optical transition, M^(n) different states can be uniquelydefined. In the case of M=2 where the two states could be the presenceor absence of the semiconductor nanocrystal, the encoding scheme wouldthus be defined by a base 2 or binary code. In the case of M=3 where thethree states could be the presence of a semiconductor nanocrystal at twodistinguishable intensities or its absence, the encoding scheme would bedefined by a base 3 code. Herein, such base M codes where M>2 are termedhigher order codes. The advantage of higher order codes over a binaryorder code is that fewer identifiers are required to encode the samequantity of information.

[0067] As one of ordinary skill in the art will realize, the ability todevelop a higher order encoding system is dependent upon the number ofdifferent intensities capable of detection by both the hardware and thesoftware utilized in the decoding system. In particularly preferredembodiments, each discrete emission or color, is capable of beingdetectable at two to twenty different intensities. In a particularlypreferred embodiment wherein ten different intensities are available, itis possible to employ a base 11 code comprising the absence of thesemiconductor nanocrystal, or the detection of the semiconductornanocrystal at 10 different intensities.

[0068] Clearly, the advantages of the semiconductor nanocrystals, namelythe ability to observe discrete optical transitions at a plurality ofintensities, provides a powerful and dense encoding scheme that can beemployed in a variety of disciplines. In general, one or moresemiconductor nanocrystals may act as a barcode, wherein each of the oneor more semiconductor nanocrystals produces a distinct emissionsspectrum. These characteristic emissions can be observed as colors, asshown in FIG. 1, if in the visible region of the spectrum, or may alsobe decoded to provide information about the particular wavelength atwhich the discrete transition is observed. Likewise, for semiconductornanocrystals producing emissions in the infrared or ultraviolet regions,the characteristic wavelengths that the discrete optical transitionsoccur at provide information about the identity of the particularsemiconductor nanocrystal, and hence about the identity of or locationof the item or matter of interest.

[0069] An example of a specific system for automated detection thatcould be employed for use in the present invention includes, but is notlimited to, an imaging scheme comprising an excitation source, amonochromator (or any device capable of spectrally resolving the image,or a set of narrow band filters) and a detector array. In oneembodiment, the apparatus would consist of a blue or UV source of light,of a wavelength shorter than that of the luminescence detected. Thiscould be a broadband UV light source, such as a deuterium lamp with afilter in front; the output of a white light source such as a xenon lampor a deuterium lamp after passing through a monochromator to extract outthe desired wavelengths; or any of a number of continuous wave (cw) gaslasers, including but not limited to any of the Argon Ion laser lines(457, 488, 514, etc. nm), a HeCd laser; solid state diode lasers in theblue such as GaN and GaAs (doubled) based lasers or the doubled ortripled output of YAG or YLF based lasers; or any of the pulsed laserswith output in the blue, to name a few. The luminescence from the dotswould be passed through an imaging subtracting double monochromator (ortwo single monochromators with the second one reversed from the first),for example, consisting of two gratings or prisms and a slit between thetwo gratings or prisms. The monochromators or gratings or prisms canalso be replaced with a computer controlled color filter wheel whereeach filter is a narrow band filter centered at the wavelength ofemission of one of the dots. The monochromator assembly has moreflexibility because any color can be chosen as the center wavelength.Furthermore, a CCD camera or some other two dimensional detector recordsthe images, and software color codes that image to the wavelength chosenabove. The system then moves the gratings to a new color and repeats theprocess. As a result of this process, a set of images of the samespatial region is obtained and each is color-coded to a particularwavelength that is needed to analyze the data rapidly.

[0070] In another preferred embodiment, the apparatus is a scanningsystem as opposed to the above imaging scheme. In a scanning scheme, thesample to be analyzed is scanned with respect to a microscope objective.The luminescence is put through a single monochromator or a grating orprism to spectrally resolve the colors. The detector is a diode arraythat then records the colors that are emitted at a particular spatialposition. The software then ultimately recreates the scanned image anddecodes it.

[0071] More particularly, specific preferred embodiments for uses of theinventive encoding system are described with reference to the followingexamples. These examples are provided only for the purposes ofillustration and are not intended to limit the scope of the presentinvention.

[0072] Applications to Fluid Dynamics and Microfluidics

[0073] In one particularly preferred embodiment, the inventive systemcan be utilized to track or trace the location of a component ofinterest. For example, fluid dynamics involves generally monitoring theinteraction between different fluid components, and thus the location ofindividual molecules of the desired fluid provides valuable informationabout the effectiveness of and the degree of interaction betweenseparate components, specifically the controlled movement and mixing ofcomponents. In the method of the present invention, one of ordinaryskill in the art will realize that the semiconductor nanocrystals can beappropriately functionalized to facilitate interaction with the desiredcomponent of interest (so that the semiconductor nanocrystals arecompatible with the fluid they are intended to act as tracers for), asdiscussed in detail earlier, and subsequent mixing of the individualcomponents can be effected. In but one example, if the interactionbetween two fluids having different characteristics, such as pyridineand dimethylsulfoxide, is being studied, the surface of thesemiconductor nanocrystals can be modified with pyridine ordimethylsulfoxide moieties to ensure association of or compatibility ofa particular size distribution of semiconductor nanocrystals with theappropriate fluid.

[0074] Because each the semiconductor nanocrystals are specificallyassociated with a particular component, it is then possible to take aphotograph of the reaction mixture with a ultraviolet lamp and, basedupon the discrete optical emissions produced from the semiconductornanocrystals, gain information about the degree of interaction of theindividual components. FIG. 3 depicts a general method for fluiddynamics, wherein two streams of fluid (10) and (20), represented by Xand Y in FIG. 3, are introduced into a reaction chamber (30) and themixing of the fluids is monitored by taking a “picture” at a given timewith an excitation source to observe the position of the semiconductornanocrystals associated with the particular fluid. FIG. 3B depicts anenlargement of the reaction chamber (30) and shows the association ofthe semiconductor nanocrystals (40) with a particular fluid of interest(10). One of ordinary skill in the art will realize that the ability ofthe semiconductor nanocrystals to produce discrete transitions enablesthe mixing of N components, where N represents the number of discretetransitions.

[0075] One particularly preferred application for this system forlocation identification described above is the monitoring ofmicrofluidic molecular systems (MicroFlumes). These microfluidic systemsperform multiple reaction and analysis techniques in one microinstrumentfor specificity and validation, they are completely automated, theycontain multiple parallel reaction paths (as opposed to the sequentialanalysis required today) and provide the capability for hundreds ofoperations to be performed without manual intervention. (Seehttp://web-ext2.darpa.mil/eto/mFlumes/index.html)

[0076] The semiconductor nanocrystal can be used as in the generalmethod described above, where each semiconductor nanocrystal orcombination thereof can be associated with or attached to a specificcomponent of interest and upon mixing of the various components, andproviding a primary light source, can provide information about thedegree and type of interaction between the different components. One ofordinary skill in the art will realize that the inventive encodingsystem is not limited to the fluid dynamics applications describedabove; rather the inventive system is capable of being utilized in anysystem where the tracking of the location of a component or item, suchas a gas, liquid, solid, or consumer item (such as dry-cleaned clothing)is desired.

[0077] Identification of an Object

[0078] The system of the present invention can also be utilized toidentify specific objects including, but not limited to, jewelry, paper,biomolecules such as DNA, vehicles and identification cards. Forexample, the semiconductor nanocrystals can be appropriatelyfunctionalized for incorporation into or attachment to the surface ofthe object of interest, as discussed above, and as shown in FIG. 4. FIG.4A depicts the incorporation of the semiconductor nanocrystals into anitem of interest (50), wherein the surface of semiconductor nanocrystalhas been modified to enable incorporation into the item of interest.FIG. 4B depicts the coating of a semiconductor nanocrystal composition(80) into an item of interest (90), wherein the surface of thesemiconductor nanocrystal (70) is modified to interact with thecomposition medium X (60). In but one example, the semiconductornanocrystal surface may be functionalized with a specific percentage ofamine moieties, thus enabling incorporation into paper, which iscomprised of carbohydrate moieties. In other embodiments, thesemiconductor nanocrystals may be appropriately functionalized withmoieties such as styrene or acrylate to enable incorporation intopolymers. The polymers containing the identification units can then becoated onto, or incorporated within specific items such asidentification cards. The ease with which the semiconductor nanocrystalscan be incorporated into the item and the fact that the semiconductornanocrystal based “barcode” is invisible, provides a useful system forlabeling objects. The ability of the semiconductor nanocrystal “barcode”system to encode large amounts of information, and thus large numbers ofitems, provides an advantage over existing barcode or microparticlesystems discussed previously. The identification of the item of interestfrom a collection of items can be effected by providing a primary lightsource and correlating the spectral emissions to a collection ofsemiconductor nanocrystals that encode a particular item of interest. Inanother particularly preferred embodiment, the present system may beutilized to keep track of the identity of biomolecules, such as DNAsequences, while they are subjected to reaction processes and chemicalmanipulations. The biomolecules, or DNA sequences, could be “tagged”themselves, or, alternatively, the biomolecules could be attached to asupport, wherein the support is “tagged” with one or more sizes ofsemiconductor nanocrystals encoding the identity of the DNA sequence.

[0079] Encoding Combinatorial Libraries

[0080] In another particularly preferred embodiment, the inventivesemiconductor nanocrystals may also be used to identify a particularcompound in a library of compounds by encoding a particular reactionsequence employed for each of the compounds in the synthesis of complexcombinatorial libraries, and thus acting as an identifier. Because ofthe desirability for the production of large numbers of complexcompounds, particularly using a split and pool method, the developmentof encoding techniques to identify each compound of interest has becomeimportant. Because of the small quantity of final product or compoundproduced from such methods, identifying these products would generallynot be feasible. However, by associating each stage or combination ofstages of the serial synthesis with an identifier which defines thechoice of variables such as reactant, reagent, reaction conditions, or acombination of these, one can use the identifiers to define the reactionhistory of each definable and separable substrate. The spectral analysisof the semiconductor nanocrystals allows for ready identification of thereaction history. For example, one can determine a characteristic of aproduct of a synthesis, usually a chemical or biological characteristicby various screening techniques, and then identify the reaction historyand thereby the structure of that product, which has the desiredcharacteristic, by virtue of the semiconductor nanocrystal “barcode”associated with the product.

[0081] The use of the instant multiple identification system avoids thenecessity of carrying out a complicated cosynthesis which reduces yieldsand requires multiple protecting groups, and avoids the necessity ofusing sequenceable tags which are necessarily chemically labile. Boththe necessity of multiple protecting groups and the intrinsicinstability of all known sequenceable tagging molecules (i.e. nucleicacid or peptide oligomers) severely limit the chemistry which may beused in the synthesis of the library element or ligand. Additionally,the present system avoids the need to cleave the tags from the solidsupport for analysis.

[0082] Moreover, the advantage of providing a distinct andnon-overlapping resonance, capable of detection at differentintensities, enables the use of a binary encoding system or higher. Forexample, the absence or presence of a particular size semiconductornanocrystal could be used in a binary system. However, the use ofdifferent intensities, of the same color enables the use of a higherorder encoding system, each color intensity encoding a particularcharacteristic.

[0083] According to the method of the present invention, the products tobe encoded include, but are not limited to biomolecules (such aspeptides and oligonucleotides, organic compounds, and inorganiccompounds and catalysts resulting from combinatorial synthesis.Exemplary combinatorial libraries that can be synthesized using thepresent encoding method include, but are not limited to peptidelibraries, peptidomimetics, carbohydrates, organometallic catalysts andsmall molecule libraries (For examples see, Kahne, D. Curr. Opin. Chem.Biol., 1997, 1, 130; Hruby et al., Curr. Opin. Chem. Biol., 1997, 1,114; Gravert et al., Curr. Opin. Chem. Biol., 1997, 1, 107).

[0084] In a particularly preferred embodiment, a solid phase synthesistechnique such as split and pool synthesis is utilized, in which thedesired scaffold structures are attached to the solid phase directly orthough a linking unit, as discussed above. Advantages of solid phasetechniques include the ability to conduct multi-step reactions moreeasily and the ability to drive reactions to completion because excessreagents can be utilized and the unreacted reagent washed away. Perhapsone of the most significant advantages of solid phase synthesis is theability to use a technique called “split and pool”, in addition to theparallel synthesis technique, developed by Furka. (Furka et al., Abstr.14th Int. Congr. Biochem., Prague, Czechoslovakia, 1988, 5, 47; Furka etal., Int. J. Pept. Protein Res. 1991, 37, 487; Sebestyen et al., Bioorg.Med. Chem. Lett., 1993, 3, 413.) In this technique, a mixture of relatedcompounds can be made in the same reaction vessel, thus substantiallyreducing the number of containers required for the synthesis of verylarge libraries, such as those containing as many as or more than onemillion library members. As an example, the solid support scaffolds canbe divided into n vessels, where n represents the number species ofreagent A to be reacted with the scaffold structures. After reaction,the contents from n vessels are combined and then split into m vessels,where m represents the number of species of reagent B to be reacted withthe scaffold structures. This procedure is repeated until the desirednumber of reagents is reacted with the scaffold structures to yield theinventive library.

[0085] The semiconductor nanocrystals of the present invention can bereadily attached to a solid support. A solid support, for the purposesof this invention, is defined as an insoluble material to whichcompounds are attached during a synthesis sequence. The use of a solidsupport is advantageous for the synthesis of libraries because theisolation of support-bound reaction products can be accomplished simplyby washing away reagents from the support-bound material and thereforethe reaction can be driven to completion by the use of excess reagents.A solid support can be any material that is an insoluble matrix and canhave a rigid or semi-rigid surface. Exemplary solid supports include butare not limited to pellets, disks, capillaries, hollow fibers, needles,pins, solid fibers, cellulose beads, pore-glass beads, silica gels,polystyrene beads optionally cross-linked with divinylbenzene, graftedco-poly beads, poly-acyrlamide beads, latex beads, dimethylacrylamidebeads optionally crosslinked with N—N′-bis-acryloylethylenediamine, andglass particles coated with a hydrophobic polymer. In one particularlypreferred embodiment, a Tentagel amino resin, a composite of 1) apolystyrene bead crosslinked with a divinylbenzene and 2) PEG(polyethylene glycol), is employed for use in the present invention. Thesemiconductor nanocrystals of the present invention can readily befunctionalized with styrene and thus can be incorporated into Tentagelbeads, or the semiconductor nanocrystals may be functionalized with acarboxylate moiety and can be readily attached to the Tentagel supporthaving an amine moiety through an amide linkage. Tentagel is aparticularly useful solid support because it provides a versatilesupport for use in on-bead or off-bead assays, and it also undergoesexcellent swelling in solvents ranging from toluene to water.

[0086] The semiconductor nanocrystals therefore identify each reactionstage that an individual solid support has experienced, and records thestep in the particular synthesis series, as shown in FIG. 5. FIG. 5depicts the attachment of three different reagents A, B, and C (120) toa solid support, and the attachment of the identification unit (140) tothe solid support (100) via a linkage (90). The supports are then pooledtogether (130) and split for reaction with reagents D, E, and F.Attachment of appropriate identification units for each of thesereagents enables the encoding of this particular reaction stage asobserved previously for reagents A, B, and C. In this particularembodiment, the tags may be attached to all (or most) of the solidsupports immediately before, during, or immediately after the reactionstage, depending on the particular chemistry used in a given reactionsequence.

[0087] In another preferred embodiment, the beads can be labeled withthe semiconductor nanocrystals prior to reaction of the beads with anyreagents, and as the beads are split in the split and pool process, thebeads are read before being added to a new (split stage) container tokeep track of the particular reaction at that particular stage in thesynthesis.

[0088] Once the synthesis is complete, the library of compounds can thenbe screened for biological activity and the supports having a compoundof interest can then be analyzed directly (on-bead analysis) to provideinformation about the reaction stages and history of the synthesis.

[0089] Although the method described above is with reference to splitand pool combinatorial techniques, one of ordinary skill in the art willrealize that the present encoding scheme is not limited to split andpool methods; rather the inventive encoding scheme can be utilized inany combinatorial or other reaction scheme such as parallel synthesis,or synthesis of compounds on an array, to name a few.

[0090] Genomics Applications:

[0091] In another particularly preferred embodiment of the presentinvention, the inventive system can be utilized to gain informationabout genetic information from oligonucleotide fragments. In general, ithas been desirable to understand genetic variation and its consequenceson biological function, and in order to do this, an enormous comparativesequence analysis must be carried out. Because each DNA strand has thecapacity to recognize a uniquely complementary sequence through basepairing, the process of recognition, or hybridization, is highlyparallel, as every nucleotide in a large sequence can in principle bequeried at the same time.

[0092] DNA chip technology has been an important tool for genomicsapplications. Single nucleotide polymorphisms (SNPs) are the mostfrequently observed class of variations in the human genome. Detectingthe differences between alleles of genes is a significant goal ofmedical research into genetic diseases and disorders. (For example,sickle cell anemia, colon cancer, BRCA1). Current technology has allowedfor large scale screening of DNA sequences for mutations in thesequence. This technology involves the creation of DNA “chips” thatcontain high-density arrays of DNA sequences (e.g. STSs) covalentlybound at specific locations on a surface (glass). A set of fouroligonucleotides of identical sequence except for a single basealteration (A, G, T, or C) near the center is used to compare twoalleles of a gene. Single nucleotide differences between alleles at theposition complementary to altered sites in the set of fouroligonucleotides will allow one oligonucleotide to hybridizepreferentially over the other three. Detecting which oligonucleotidehybridizes to the sample DNA will then identify the sequence of thepolymorphism. By creating sets of these four oligonucleotides that areshifted over by one nucleotide each, a researcher can scan a largenumber of basepairs for single nucleotide polymorphisms.

[0093] The system of the present invention, in contrast to fluorescentlylabeled probes used in the existing methods, is capable of not onlyacting as a probe for identification of a desired sequence, but is alsocapable of encoding information about the sequence itself. Because theinventive identification system is capable of providing both a probe andidentifier, ordered arrays are not necessary for accessing geneticinformation, although the inventive system can still be used intraditional arrays. Instead, a collection of beads, for example, can beassembled with the desired labeled DNA fragments, wherein said beads arealso encoded with information about the particular sequence. Uponbinding, the oligonucleotide that hybridizes to the sample DNA can bedetected by scanning the sample to identify the semiconductornanocrystal labeled probe, while at the same time the sequenceinformation can then be decoded by analyzing the semiconductornanocrystal “barcode”.

We claim:
 1. A library of compounds, wherein each compound in thelibrary is bound to an individual support, each support havingassociated therewith one or more populations of semiconductornanocrystals, each population having a distinct characteristic spectralemission.
 2. The library of claim 1, wherein each nanocrystal membercomprises: a core comprising a first semiconductor material; and a shelllayer overcoating the core, the shell comprising a second semiconductormaterial having a band gap greater than that of the core, wherein thefirst semiconductor material and the second semiconductor material arethe same or different.
 3. The library of claim 1, wherein thecharacteristic spectral emission is a wavelength of emitted light, anintensity of emitted light, or both a wavelength and an intensity ofemitted light.
 4. A method for identifying a compound having acharacteristic of interest comprising: (a) providing a library of membercompounds, wherein each member of said library of compounds is attachedto a support, and wherein each support also has attached thereto orembedded therein one or more populations of semiconductor nanocrystals,each population having distinct characteristic spectral emissions; (b)testing each member of said library of compounds to identify compoundshaving a characteristic of interest; (c) subjecting each support to alight source to obtain the characteristic spectral emission; and (d)correlating the spectral emission with the identity of the compoundhaving the characteristic of interest.
 5. A method for identifying amolecule having a characteristic of interest comprising: providing afirst library of one or more member molecules, wherein each member ofsaid first library is attached to a first support having attachedthereto or embedded therein one or more first populations ofsemiconductor nanocrystals, each first population having a distinctcharacteristic first spectral emission; providing a second library ofone or more member molecules, wherein each member of said second libraryis attached to a second support having attached thereto or embeddedtherein one or more second populations of semiconductor nanocrystals,each second population having a distinct characteristic second spectralemission, and wherein the second spectral emission is distinct from thefirst spectral emission; contacting said first library of molecules withsaid second library of molecules; and observing the first and secondspectral emissions, wherein said first and second spectral emissionsprovide information about which of the molecules from the second libraryof molecules are associated with said first library of molecules, andprovides information about the identity of the molecule from said firstlibrary of molecules.
 6. The method of claim 5, wherein the firstlibrary of molecules includes a protein, an oligonucleotide, or a sugarmoiety.
 7. The method of claim 5, wherein the second library ofmolecules includes a protein, an oligonucleotide, or a sugar moiety. 8.The method of claim 6, wherein the second library of molecules includesa protein, an oligonucleotide, or a sugar moiety.
 9. The method of claim5, wherein the first support is a first bead.
 10. The method of claim 5,wherein the second support is a second bead.
 11. The method of claim 9,wherein the second support is a second bead.
 12. The library of claim 1,wherein each individual support is a bead, a pellet, a disk, acapillary, a hollow fiber, a needle, a solid fiber, a cellulose bead, apore-glass bead, a silica gel, a polystyrene beads optionallycross-linked with divinylbenzene, a grafted co-poly bead, apoly-acrylamide bead, a latex bead, a dimethylacrylamide bead optionallycross-linked with N,N′-bis-acryloyl ethylene diamine, a glass particlecoated with a hydrophobic polymer, or a low molecular weightnon-cross-linked polystyrene.
 13. The library of claim 1, wherein atleast one compound in the library is a polypeptide, an oligonucleotide,or a sugar moiety.
 14. The method of claim 4, wherein each nanocrystalcomprises: a core comprising a first semiconductor material; and a shelllayer overcoating the core, the shell comprising a second semiconductormaterial having a band gap greater than that of the core, wherein thefirst semiconductor material and the second semiconductor material arethe same or different.
 15. The method of claim 4, wherein thecharacteristic spectral emission is a wavelength of emitted light, anintensity of emitted light, or both a wavelength and an intensity ofemitted light.
 16. The method of claim 4, wherein at least one member ofthe library is a polypeptide.
 17. The method of claim 4, wherein atleast one member of the library is a nucleic acid.
 18. The method ofclaim 4, wherein at least one member of the library is a sugar moiety.19. A method for identifying a compound having a characteristic ofinterest comprising: providing a library of member compounds, whereineach member of said library of compounds is attached to a support, andwherein each support also has attached thereto, embedded therein, orassociated therewith one or more populations of semiconductornanocrystals, each population having a distinct characteristic spectralemission; subjecting one or more supports to a light source to detect acharacteristic spectral emission; and correlating the spectral emissionwith a member compound.
 20. The method of claim 19, further comprisingtesting one or more members of said library of compounds for thepresence of a characteristic of interest.
 21. The method of claim 20,wherein correlating includes identifying a member compound having acharacteristic of interest.
 22. The method of claim 19, wherein at leastone member of the library is a polypeptide.
 23. The method of claim 19,wherein at least one member of the library is a nucleic acid.
 24. Themethod of claim 19, wherein at least one member of the library is asugar moiety.
 25. The method of claim 19, wherein each nanocrystalcomprises: a core comprising a first semiconductor material; and a shelllayer overcoating the core, the shell comprising a second semiconductormaterial having a band gap greater than that of the core, wherein thefirst semiconductor material and the second semiconductor material arethe same or different.
 26. A chemical library comprising a plurality ofmember chemicals, wherein each member chemical is bound to a support,each support having associated therewith one or more populations ofsemiconductor nanocrystals, each population having a distinctcharacteristic spectral emission.
 27. The library of claim 26, whereinat least one member of the library is a polypeptide.
 28. The library ofclaim 26, wherein at least one member of the library is a nucleic acid.29. The library of claim 26, wherein at least one member of the libraryis a sugar moiety.
 30. The library of claim 26, wherein each member ofthe library includes a nucleic acid.
 31. The library of claim 26,wherein each nanocrystal comprises: a core comprising a firstsemiconductor material; and a shell layer overcoating the core, theshell comprising a second semiconductor material having a band gapgreater than that of the core, wherein the first semiconductor materialand the second semiconductor material are the same or different.
 32. Thelibrary of claim 26, wherein the characteristic spectral emission is awavelength of emitted light, an intensity of emitted light, or both awavelength and an intensity of emitted light.
 33. The library of claim26, wherein the each support is a bead, a pellet, a disk, a capillary, ahollow fiber, a needle, a solid fiber, a cellulose bead, a pore-glassbead, a silica gel, a polystyrene beads optionally cross-linked withdivinylbenzene, a grafted co-poly bead, a poly-acrylamide bead, a latexbead, a dimethylacrylamide bead optionally cross-linked withN,N′-bis-acryloyl ethylene diamine, a glass particle coated with ahydrophobic polymer, or a low molecular weight non-cross-linkedpolystyrene.
 34. A library of nucleic acids comprising a plurality ofnucleic acids, wherein each nucleic acid in the library is bound to anindividual support, each support having associated therewith one or morepopulations of semiconductor nanocrystals, each population having adistinct characteristic spectral emission.
 35. The library of claim 34,wherein each nanocrystal comprises: a core comprising a firstsemiconductor material; and a shell layer overcoating the core, theshell comprising a second semiconductor material having a band gapgreater than that of the core, wherein the first semiconductor materialand the second semiconductor material are the same or different.
 36. Thelibrary of claim 34, wherein the characteristic spectral emission is awavelength of emitted light, an intensity of emitted light, or both awavelength and an intensity of emitted light.
 37. A library ofpolypeptides comprising a plurality of polypeptides, wherein eachpolypeptide in the library is bound to an individual support, eachsupport having associated therewith one or more populations ofsemiconductor nanocrystals, each population having a distinctcharacteristic spectral emission.
 38. The library of claim 37, whereineach nanocrystal comprises: a core comprising a first semiconductormaterial; and a shell layer overcoating the core, the shell comprising asecond semiconductor material having a band gap greater than that of thecore, wherein the first semiconductor material and the secondsemiconductor material are the same or different.
 39. The library ofclaim 37, wherein the characteristic spectral emission is a wavelengthof emitted light, an intensity of emitted light, or both a wavelengthand an intensity of emitted light.